Arrayed display systems are increasingly being used to provide composite images that are larger, brighter, and have higher resolution than, e.g., a single image displayed on a desktop monitor or a television. In arrayed display systems, multiple images are typically placed adjacently to one another horizontally or vertically to form a single composite image. The images are typically generated by a computer, specialty cameras, or specially prepared media, which may include a movie film divided into multiple portions and stored in multiple specially formatted DVDs, laser disks or multi-channel video servers. When using an arrayed display system, it is highly desirable to minimize appearance of segregation between the image segments that are arrayed to form the composite image.
The arrayed display systems include projector-based display systems made up of multiple projectors to provide a projected composite image. The projector-based arrayed display systems often utilize edge blending technology in order to create a single seamless composite image. In edge blending technology, to make a seamless composite image from multiple projectors, a portion of the image from each projector is typically overlapped with a portion of the image from an adjacent projector and a smoothing correction or ramping factor on each side of the overlapped region is used to blend the brightness of the overlapping images together so that they appear uniform and seamless.
Examples of edge blending technology are described in U.S. Pat. No. 4,974,073 entitled xe2x80x9cSeamless Video Display,xe2x80x9d U.S. Pat. No. 5,136,390 entitled xe2x80x9cAdjustable Multiple Image Display Smoothing Method and Apparatus,xe2x80x9d and U.S. Pat. No. 6,115,022 entitled xe2x80x9cMethod and Apparatus for Adjusting Multiple Projected Raster Images,xe2x80x9d all of which are fully incorporated by reference herein.
These patents disclose, but are not limited to, methods for defining the raster and overall projection regions as well as a method for defining the edges of the overlapped region for edge blending purposes. They further describe detailed methods for ramping and adjusting the bright overlapping portions of the images in order to create apparently seamless images. By defining the overlapped regions in these patents, non-overlapped regions are also defined by default.
The projector technologies have progressed from systems that were based on cathode ray tube (CRT) projectors to various formats of display engines (projectors) that include Liquid Crystal Display (LCD), Image Light Amplification (ILA-Hughes/JVC), Liquid Crystal on Silicon (Lcos/Various), Digital Light Processing or Digital Micro Mirrors (DLPxe2x80x94Texas Instruments) projectors and others. The display engines that are not based on the CRT technology are sometimes referred to as non-CRT projectors or non-CRT display engines.
These non-CRT projectors typically create a projected image by applying a constant light source to a medium with variable reflectivity or translucence. The use of variable reflectivity (or variable translucence) is different from the method used in the CRT technology, which uses an electron beam to excite phosphor in order to create a variable luminance using the cathode ray tube.
Since the CRT provides a variable luminance based on the strength of the electron beam, the luminance of the CRT can be turned all the way down to where the CRT has zero photonic output. A perfect non-CRT projector with a constant light source may also be able to tune the light or photonic output to zero. However, in practice, currently available non-CRT projectors typically provide a residual amount of light and generate residual brightness even when the desired image is fully black. The residual light that is inherent to typical non-CRT projectors can be referred to as an r factor or residual factor, which is a measure of photonic leakage per unit area of the projected image.
The value of the residual factor in the overlapped region between two adjacent images in a projector array is approximately equal to the sum of the values of the residual factors of the two adjacent images or Ra+Rb, where Ra is the residual factor of the first adjacent image and Rb is the residual factor of the second adjacent image. In another example where the projectors are adjacent in two directionsxe2x80x94side by side as well as over and under, and assuming that the residual factors of the projectors are Ra, Rb, Rc and Rd, respectively, the residual factor in the region where all four images overlap is approximately equal to the sum of the residual factors, i.e., Ra+Rb+Rc+Rd. Thus, a relatively bright seam or a region may appear in the overlapped areas of a projection array when the composite image is displaying a dark scene.
Thus, edge blending technology typically does not work well with non-CRT projectors that cannot be tuned to create zero photonic output when the image is to be at a very dark gray level, or fully black. Therefore, when using non-CRT projectors, use of edge blending technology has a limitation, and a method of making the minimum black level across the composite image uniform may be needed especially when the video signal going to the projector is already at a minimum, but the projector is still leaking photons. In this case, the difference in residual brightness between non-overlapped and overlapped regions cannot be resolved through further attenuation of the signal in the overlap.
Therefore, it is desirable to develop a method of reducing the non-uniformity in the overlapped regions caused by the residual photonic leakage which complements edge blending technology in order to generate an apparently seamless composite image when, for example, non-CRT projectors are used.
In an embodiment according to the present invention, a method of generating an apparently seamless composite image from a plurality of video signals is provided. The video signals correspond to discrete images, and at least one of the discrete images has an overlap with at least one other of the discrete images. The video signals are edge blended to reduce the appearance of a seam in the overlap between the corresponding discrete images. Then, the video signals are adjusted to raise minimum black levels of non-overlapped regions of the corresponding discrete images, without affecting the rest of the video signals, to match the minimum black level of the overlap.
In another embodiment of the present invention, a method of smoothing the brightness and minimum black level of two adjoining overlapping video images is provided. The video images are produced from two discrete video signals. The signals comprise a plurality of detail elements, each detail element having a brightness component. A predetermined set of smoothing factors is applied to the brightness components of the detail elements of the two video signals, each smoothing factor being associated with a the detail element to which it is applied. The images, as modified by the smoothing factors, are projected onto a display. Individual smoothing factors are modified independently of one another in response to the appearance of the projected display. A representation of the smoothing factor modifications is stored. The smoothing factors are used to adjust the brightness components of the detail elements in an overlapped region to lower a maximum bright level of the overlapped region to match maximum bright levels of non-overlapped regions, and to adjust the brightness components of the detail elements in the non-overlapped regions to raise minimum black levels to match the minimum black level of the overlapped region.
In yet another embodiment of the present invention, a system for adjusting video signals representing an array of raster images to compensate for projection defects is provided. The system includes a plurality of projectors, which are used to display the array of raster images to form a composite projected image. The system also includes an array of smoothing factors, each smoothing factor being associated with a portion of the composite projected image. Further, the system includes means for applying smoothing factors to the video signals to remove the projection defects resulting from display of the array of raster images. The projection defects comprise differences in maximum bright levels and minimum black levels between overlapped and non-overlapped regions of the composite projected image.
In an alternate embodiment of the present invention, a method of generating an apparently seamless composite image from a plurality of video signals is provided. The video signals correspond to discrete images, and at least one of the discrete images has an overlap with at least one other of the discrete images. Portions of the video signals corresponding to non-overlapped regions are adjusted to raise the brightness of the non-overlapped regions to match the brightness of the overlap.